Smart packaging is an important consideration in the manufacture of an implantable device. The device housing has to be robust both mechanically and chemically to provide adequate protection from the harsh environment of the human body and, at the same time must provide protection to the body in which it is implanted.
In one instance, as disclosed in U.S. Pat. No. 5,013,396 to Wise et al., an ultraminiature capacitive pressure sensor having a silicon diaphragm and rim structure is made with a simple double-diffusion process. This novel diaphragm and rim structure is part of a silicon transducer chip which is electrostatically bonded to a glass support plate prior to removal of all of the wafer except for the diaphragm and rim structure. The novel diaphragm and rim structure features a very small rim area, thus allowing the transducer to be constructed in ultraminiature form. Thus, a capacitive pressure sensor can be mounted, for example, in a 0.5 millimeter OD multisite cardiac catheter suitable for measuring blood pressure gradients inside the coronary artery of the heart. The silicon pressure transducer preferably includes supporting interface circuitry on a chip fastened to the same glass support plate as the diaphragm and rim structure. However, no concern is expressed in the disclosure for protecting the pressure sensor in the body.
U.S. Pat. No. 5,674,258 to Henschel et al. discloses a packaged integrated accelerometer. In this instance, a method is provided for surface mounting a piezoceramic accelerometer directly to a hybrid circuit within a hermetically sealed pacemaker housing.
U.S. Pat. No. 5,843,135 to Weijand et al. discloses a pacing lead incorporating both a sensor, e.g., a pressure sensor, and an electrode for pacing and sensing, the lead being connected to a pacemaker which delivers pacing pulses to the electrode, the pacemaker also receiving and processing cardiac signals from the electrode and sensor information from the sensor. Again, however, there is no mention of packaging for protection of the sensor or of the body.
U.S. Pat. Nos. 5,911,738 and 6,038,475, both to Sikorski et al., provide a method of and apparatus for coupling an accelerometer within a cardiac pacemaker, and by providing a structure which improves substantially the shock survivability of same. In this instance, an accelerometer assembly comprises at least three electrodes electrically isolated from one another in a piezoelectric sub-assembly. The sub-assembly is covered at least partially with an external electrically conductive layer that has been laser scribed or cut to provide electrical isolation of each of the electrodes from the other electrodes. At least one of the electrodes is an internal electrode disposed between opposing sheets of piezoelectric material, and forms an internal electrically conductive layer to which electrical connection is possible from the external surface of the sub-assembly. The remaining two electrodes are external electrodes and may be connected electrically in parallel across the internal electrode to provide a high output signal.
In U.S. Pat. No. 6,223,081 to Kerver, a pacemaker contains a pressure sensor in combination with a pacing lead which connects stimulus pulses to the patient's heart and which is operatively connected to the pacemaker so as to transmit cardiac pressure signals to the pressure sensor. However, once again, there is no mention of or concern for protective packaging of the pressure sensor.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.